This is first and most popular application of multichannel IR remote control where microcontroller 89C51 is used to switch ON/OFF four different home appliances (like tubelight, bulb, night lamp etc.). One can connect any device which has ON/OFF operation and which works on available domestic supply.
The figure in circuit diagram tab1 shows circuit diagram of remote control for home appliances.
This is just an extension to last project. Port P2 is utilized to switch the particular relay on/off depending upon the key pressed. Port P2 Switches relays through JK flip-flop ICs. Both JK flip-flop ICs (74LS107) connected as T flip-flop. The o/p of port pins are given as clock and reset i/p to these ICs. It’s Q output toggles every time when it receives clock pulse. Two ICs gives total four Q outputs so total four relays can be switched on or off.
Suppose you press any switch from remote control. Signal will be demodulated by sensor and given to micro-controller. Micro-controller will detect the frequency and depending upon which key is pressed it will give clock pulse to that particular T flip-flop. So it’s o/p will toggle means if it was low then it will be high. Now when you press same key again the o/p of flip flop again toggle and now it will be low.
Relay Firing Circuit
As this o/p is utilized to switch relay the relay will be switched (from N/C to N/O) when o/p of flip flop is high and vice versa. The typical relay firing circuit is as shown in circuit diagram tab2.
(Note:- this is single section of relay driver board. There are similar four sections in complete circuit)
Two transistors (2N2222) are connected as Darlington pair to provide sufficient current to switch the relay. Any 230V AC device like fan, bulb, tube light, table lamp etc. can be connected between C (common) and N/O (normally open) contacts of relay with 230V supply as shown in figure.
Filed Under: Electronic Projects